The present invention relates to a method and device for conditioning a received signal that transmits coded data.
When transmitted coded data is to be conditioned after receipt, the receiving device must have some information regarding how the coding was executed at the transmitting end, so that the signal can be decoded quickly and reliably. Many coding processes are known (e.g. binary, PWM, AM, FM). Since coded data usually are transmitted time-serially, the time base on which the signals were coded has to be known for certain coding processes, e.g. for binary signals or PWM (pulse-width modulation), so that the signals can be decoded correctly at the receiving end.
FR-A-2725 091 discloses a process for synchronizing coded data, wherein a synchronization sequence is sent first so that the recipient can determine the transmission time of the signal, followed by a sequence of initial signals so that the recipient can identify the starting time of the transmission. The process refers to a remote control, in particular a radio remote control for opening the doors of a motor vehicle from a distance. The process is supposed to ensure safe functioning of the remote control, even when it has a relative low output performance and there is electromagnetic interference.
A computer bus system for serial data transmission is described in U.S. Pat. No. 5 412 698, which exhibits an adaptive data separator so as to be able to recognize an optimal time constant from an interfered signal, wherein systematic differences between the arrival of leading and falling signal edges of a digital signal are to be recognized and compensated.
GB-A-2 240 241 describes a system for transmitting data with a certain data rate or frequency, which exhibits an arrangement for determining a time constant for the synchronization of the data rate of a received data signal and an output signal.
Furthermore, GB-A-2 180 712 discloses a system for optical data transmission, in which, on the basis of the coded signal, a synchronization bit at the beginning of every data block with an increased DC voltage level is used to determine the significance of the following data bits on a lower DC voltage level.
In the ITT application xe2x80x9cMethod and Circuit Arrangement for Transmitting Speed Information and Additional Dataxe2x80x9d dated Dec. 6, 1996, the transmitting-end shape of a signal that transmits data was disclosed. This was primarily designed for application in the construction of vehicles, in particular for transmitting data from an active wheel sensor to a superior control system. Such a system is illustrated schematically in FIG. 1. A sensor 107 and a brake 108 are attached to a wheel 106. The sensor 107 is an xe2x80x9cactivexe2x80x9d sensor, which means that it not only changes incoming electric signals (voltage or current), but also actively shapes signals in order to transmit information from wheel 107 to a superior device 101. The sensor 107 is connected to device 101 by means of a line 105, and the line 105 may consist of several individual lines. The sensor transmits diverse information about the wheel. At first information on the wheel speed should be transmitted. Then other information can be transmitted, e.g. temperature, wear of brake shoes or similar things. Since, on the one hand, the sensor 107 is located in a comparably xe2x80x9croughxe2x80x9d environment, i.e. directly on the wheel (vibrations, temperature fluctuations, moisture) and, on the other hand, the wiring is to be kept as simple as possible so that it is less susceptible to defects, the data transmitting process has to be designed in such a way that it works reliably despite the above-described adverse conditions.
The system in FIG. 1 shows a device for conditioning a received signal that transmits coded data 104, which is designed according to the present invention and is located in the control device 101. This is followed by a decoding device 103 and a control system 102 that, according to the signals received (also additional, not shown input signals), on the one hand provides control data for the wheel under review and on the other hand generates other data, e.g. alarms for alarm devices 111 or similar things. The control system 102 can deliver electric control signals to a brake control system 110, which in turn acts on the wheel brake 108 via a hydraulic line 109.
The signal generated in the active sensor 107 and transmitted to the device according to the invention 104 by way of line 105 can be shaped in the way described in the above-mentioned ITT application. Individual data sequences are explained on the basis of FIG. 3. FIG. 3a shows an ideal sequence, whereas FIG. 3b-d show real sequences. The signal generated by sensor 107 exhibits different pulses, i.e. wheel pulse 301 and subsequent data pulses 303. Preferably the wheel pulse 301 has a higher amplitude than one of the data pulses 303. The sequence of a wheel pulse 301 and data pulses 303 is provided periodically. Then the wheel speed can be determined through the intervals between the consecutive wheel pulses. A suitable number of data impulses 303 is transmitted between consecutive wheel pulses 301; these transmit additional information, e.g. coded in binary form, from the wheel to the device according to the invention.
When the wheel is standing still and the speed consequently is zero, the wheel pulse 301 is replaced by an auxiliary pulse 304. The auxiliary pulse 304 preferably has an amplitude that is lower than that of the wheel pulse 301 and in particular equal to that of the data pulses 303. Thus it can be differentiated from the wheel pulse 301. The auxiliary pulse 304 can be differentiated from data pulses 303 because the auxiliary pulse 304 occurs non-synchronized xe2x80x9cout of thin airxe2x80x9d, whereas the data pulses 303 are sent immediately afterwards.
During high speeds, the case shown in FIG. 3c may occur. Here a new wheel pulse 301xe2x80x2 is generated before the transmission of the data pulses 303, 303xe2x80x2 was completed. This presents no problem as far as the wheel pulse 301, 301xe2x80x2 is concerned, since it can be recognized by its high amplitude. Thus the speed information is transmitted. In the case shown in FIG. 3c, the usage or evaluation of the data can be stopped according to pulses 303, 303xe2x80x2. When the wheels are standing still, the case shown in FIG. 3c cannot occur, since the interval between the auxiliary pulses 304 is freely selectable, i.e. the interval between them is selected in such a way that all data pulses 303 can be transmitted between two auxiliary pulses 304.
The case shown in FIG. 3 illustrates a binary data transmission: each of the data pulses 303 correspond to one bit, which can be either 1 or 0. They are marked with 1 only for reasons of clarification. The bits follow one another at a certain interval of time tp. They must be sampled at the receiving end to be evaluated and decoded, so that their respective value is known. Thus, it must be known at the receiving end which time base was used for coding the data. This may become a problem when, as described above, the transmitter is used in a rough environment and the time base applied for the coding may be displaced due to the changing environmental influences. In this case, a fixed time base cannot be assumed. Instead the time base may vary, making it necessary to provide it to the transmitter from one case to another.
The above problem was described on the basis of an application in vehicle construction. It may also arise in other applications.
It is the object of the invention to disclose a method and device for conditioning a received signal that transmits coded data, with which the transmitted data can be decoded reliably.
According to the invention the data are transmitted together with information on the time base or time constant, on the basis of which the coding was carried out. At the receiving end this information about the time base or time constant is determined and the further evaluation of the data that was received is executed according to this information. Preferably the information concerning the time constant is transmitted at the beginning of the transmission. Then the information regarding the time constant also can be determined at the beginning of the evaluation, so that always the latest information can be used for evaluating the following data. In connection with xe2x80x9cfrequentlyxe2x80x9d repeated pulse curves, however, the information on a time constant obtained in a previous cycle can be used for a subsequent cycle. The obtained time constant, for example, may correspond to a bit period in the signal received or at least allow conclusions as to the bit duration when the coding was binary, for example by means of a proportional relationship. In connection with pulse width modulation the time constant obtained may refer to a mean pulse duration or similar.